1. Field of the Invention
The present invention relates to a controller of an internal combustion engine capable of switching a combustion type between spark ignition combustion and compression ignition combustion.
2. Description of the Related Art
As an internal combustion engine (hereafter referred to as engine) used for automobiles, etc., providing both improved fuel efficiency and improved exhaust performance, a compression ignition gasoline engine (hereafter referred to as compression ignition engine) which compresses an air-fuel mixture and performs ignition combustion (hereafter referred to as compression ignition combustion) is attracting attention. In comparison with spark ignition combustion in which an air-fuel mixture is ignited with sparks of an ignition plug, the compression ignition engine reduces the fuel consumption through improved efficiency by high compression, reduced pump loss, and reduced cooling loss by rapid combustion. The compression ignition engine also reduces the NOx concentration in exhaust gas through low-temperature combustion of the air-fuel mixture thus satisfying both the fuel efficiency performance and the exhaust performance.
For the application of the compression ignition engine to an automobile, it is proposed that both spark ignition combustion and compression ignition combustion be performed and the combustion type be switched therebetween to attain an engine torque required by a driver.
A technique for switching the combustion type between spark ignition combustion and compression ignition combustion is disclosed in JP-A-2004-293471. JP-A-2004-293471 discloses a technique which provides an operating region (hereafter referred to as intermediate compression ignition combustion region) in which intermediate compression ignition combustion is performed. In this region, torque fluctuations caused by variation of air volume and pump loss, etc. at the time of combustion type switching between spark ignition combustion and compression ignition combustion are reduced by setting a throttle opening to a setup value 3 that is a middle between a setup value 1 at the time of spark ignition combustion and a setup value 2 at the time of compression ignition combustion.